Try these solutions in order:

• 1.Analyze statistics (ANALYZE Table1; ANALYZE Table2;)
• 2.Disable sequential scan (SET enable_seqscan = OFF;)
• 3.Use explicit JOIN instead of , (comma join)
• 4.Use a CTE (WITH t2_indexed AS (...))
• 5.Rewrite with EXISTS or subqueries if applicable
• 6.Increase work_mem
• 7.Add/Reindex t1.uid