How do I go about easy table input without creating an application?
If I am not missing anything... Assuming you always specify the user name in such a way as to exclude possibility of multiple matches (if e.g. you decided to look the user up by a mask using LIKE rather than by a complete name), you could try inserting data into the record table using an INSERT...SELECT statement like below:

INSERT INTO testreport.records (userid)
SELECT userid
FROM testreport.r_user
WHERE username = 'specific user name';
/* or:
WHERE username LIKE 'some pattern'
- just make sure it matches the single row you meant to reference
*/