Filling GSTR 3B

Reduce Sales return from current month sales , balance you can reduce in the next month GSTR3B . Subject to time limit as per CGST act .

For example sale of this month is 1000/- and sales return is 1500/- , then reduce sales return 1000/- in this month from the current month sales , and balance sales return 500/- in the next month Sales ( GSTR3B ) , subject to time limit .

One more thing  , I want to clarify  is  form 1-1-20222  you GSTR1 and GSTR3B  must match . 

Sales : It creates GST liability.

Sales return : Reduces the gst liability or creates ITC .

If there is any error you may carry forward the excess credit