how to find the error description for the error codes found in the extended events file XEL generated by SSAS Tabular query end event
I think you should look at the [TextData] field.
Based on Microsoft doc here:
https://docs.microsoft.com/en-us/analysis-services/trace-events/errors-and-warnings-events-data-columns?view=asallproducts-allversions
it should contain the the text data associated with the error event, like the error message.
please, try this against your trace file.
    SELECT   xe_file.[FILE_NAME] AS [filepath]
        ,[ApplicationName] = xe_file.xml_data.value('(/event/data[@name=''ApplicationName'']/value)[1]','[nvarchar](128)')
        ,[BinaryData] = xe_file.xml_data.value('(/event/data[@name=''BinaryData'']/value)[1]','[varbinary](max)')
        ,[ConnectionID] = CAST(xe_file.xml_data.value('(/event/data[@name=''ConnectionID'']/value)[1]','[nvarchar](128)') AS INT)
        ,[CPUTime] = CAST(xe_file.xml_data.value('(/event/data[@name=''CPUTime'']/value)[1]','[nvarchar](128)') AS bigint)
        ,[CurrentTime] = CAST(xe_file.xml_data.value('(/event/data[@name=''CurrentTime'']/value)[1]','[nvarchar](128)') AS DATETIME2)
        ,[DatabaseName] = xe_file.xml_data.value('(/event/data[@name=''DatabaseName'']/value)[1]','[nvarchar](128)')
        ,[Duration] = xe_file.xml_data.value('(/event/data[@name=''Duration'']/value)[1]','[nvarchar](128)')
        ,[EndTime] = xe_file.xml_data.value('(/event/data[@name=''EndTime'']/value)[1]','[nvarchar](128)')
        ,[Error] = CAST(xe_file.xml_data.value('(/event/data[@name=''Error'']/value)[1]','[nvarchar](128)') AS INT)
        ,[EventClassId] = CAST(xe_file.xml_data.value('(/event/data[@name=''EventClass'']/value)[1]','[nvarchar](128)') AS INT)
        ,[EventSubclassId] = CAST(xe_file.xml_data.value('(/event/data[@name=''EventSubclass'']/value)[1]','[nvarchar](128)') AS INT)
        ,[IntegerData] = CAST(xe_file.xml_data.value('(/event/data[@name=''IntegerData'']/value)[1]','[nvarchar](128)') AS INT)
        ,[JobID] = CAST(xe_file.xml_data.value('(/event/data[@name=''JobID'']/value)[1]','[nvarchar](128)') AS INT)
        ,[NTCanonicalUserName] = xe_file.xml_data.value('(/event/data[@name=''NTCanonicalUserName'']/value)[1]','[nvarchar](128)')
        ,[ObjectID] = xe_file.xml_data.value('(/event/data[@name=''ObjectID'']/value)[1]','[nvarchar](128)')
        ,[ObjectName] = xe_file.xml_data.value('(/event/data[@name=''ObjectName'']/value)[1]','[nvarchar](128)')
        ,[ObjectPath] = xe_file.xml_data.value('(/event/data[@name=''ObjectPath'']/value)[1]','[nvarchar](128)')
        ,[ObjectReference] = xe_file.xml_data.value('(/event/data[@name=''ObjectReference'']/value)[1]','[nvarchar](128)')
        ,[ObjectType] = CAST(xe_file.xml_data.value('(/event/data[@name=''ObjectType'']/value)[1]','[nvarchar](128)') AS INT)
        ,[ProgressTotal] =  CAST(xe_file.xml_data.value('(/event/data[@name=''ProgressTotal'']/value)[1]','[nvarchar](128)') AS INT)
        ,[ServerName] = xe_file.xml_data.value('(/event/data[@name=''ServerName'']/value)[1]','[nvarchar](128)')
        ,[SessionID] = xe_file.xml_data.value('(/event/data[@name=''SessionID'']/value)[1]','[nvarchar](50)')
        ,[SessionType] = xe_file.xml_data.value('(/event/data[@name=''SessionType'']/value)[1]','[nvarchar](128)')
        ,[Severity] =  CAST(xe_file.xml_data.value('(/event/data[@name=''Severity'']/value)[1]','[nvarchar](128)') AS INT)
        ,[SPID] = CAST(xe_file.xml_data.value('(/event/data[@name=''SPID'']/value)[1]','[nvarchar](128)') AS INT)
        ,[StartTime] = CAST(xe_file.xml_data.value('(/event/data[@name=''StartTime'']/value)[1]','[nvarchar](128)') AS DATE)
        ,[Success] = CAST(xe_file.xml_data.value('(/event/data[@name=''Success'']/value)[1]','[nvarchar](128)') AS INT)
        ,[TextData] = xe_file.xml_data.value('(/event/data[@name=''TextData'']/value)[1]','[nvarchar](max)')
FROM    (
            SELECT   [FILE_NAME]
                    ,[XML_DATA] = CONVERT(XML, EVENT_DATA)
            FROM    sys.fn_xe_file_target_read_file(@trace_filepath, NULL, NULL, NULL)
        ) AS xe_file

;