The join part uses OR that's why running long I'm trying to make it faster
You may want to try a union of:

 SELECT sc.clientid
        ,sc.dictionid
        ,sc.firstname 
        ,sc.lastname
        ,sc.DB
        ,sc.DOLS
        ,sc.dlnum
        ,Cons.Description AS ConS
        ,Conc.Description AS ConC
        ,'False' as Assigned
    FROM    [monitor].[uxref] xref 
    JOIN [Monitor].[dbo].[seacc] sc
        ON xref.regid = sc.[consid] 
    LEFT JOIN [Monitor].[dbo].Reg Cons ON Cons.RegID = sc.ConsId
    LEFT JOIN [Monitor].[dbo].Reg Conc ON Conc.RegID = sc.ConcId
    WHERE xref.UserId =1000


and 

 SELECT sc.clientid
        ,sc.dictionid
        ,sc.firstname 
        ,sc.lastname
        ,sc.DB
        ,sc.DOLS
        ,sc.dlnum
        ,Cons.Description AS ConS
        ,Conc.Description AS ConC
        ,'False' as Assigned
    FROM    [monitor].[uxref] xref 
    JOIN [Monitor].[dbo].[seacc] sc
        ON xref.regid = sc.[concid] 
    LEFT JOIN [Monitor].[dbo].Reg Cons ON Cons.RegID = sc.ConsId
    LEFT JOIN [Monitor].[dbo].Reg Conc ON Conc.RegID = sc.ConcId
    WHERE xref.UserId =1000


i.e.

 SELECT sc.clientid
        ,sc.dictionid
        ,sc.firstname 
        ,sc.lastname
        ,sc.DB
        ,sc.DOLS
        ,sc.dlnum
        ,Cons.Description AS ConS
        ,Conc.Description AS ConC
        ,'False' as Assigned
    FROM    [monitor].[uxref] xref 
    JOIN [Monitor].[dbo].[seacc] sc
        ON xref.regid = sc.[consid] 
    LEFT JOIN [Monitor].[dbo].Reg Cons ON Cons.RegID = sc.ConsId
    LEFT JOIN [Monitor].[dbo].Reg Conc ON Conc.RegID = sc.ConcId
    WHERE xref.UserId =1000
 UNION
 SELECT sc.clientid
        ,sc.dictionid
        ,sc.firstname 
        ,sc.lastname
        ,sc.DB
        ,sc.DOLS
        ,sc.dlnum
        ,Cons.Description AS ConS
        ,Conc.Description AS ConC
        ,'False' as Assigned
    FROM    [monitor].[uxref] xref 
    JOIN [Monitor].[dbo].[seacc] sc
        ON xref.regid = sc.[concid] 
    LEFT JOIN [Monitor].[dbo].Reg Cons ON Cons.RegID = sc.ConsId
    LEFT JOIN [Monitor].[dbo].Reg Conc ON Conc.RegID = sc.ConcId
    WHERE xref.UserId =1000