Confusion regarding sale return

As you have received the debit note in the month of May, you will have to file net GST i.e. 15000/- in GSTR3B of May 2020. also you have to fill the debit note of 10000 details in GSTR 1 of May 2020 table no 9B and 25000 in table 4a of gstr1 of may 2020.

Thnku so much sir ....this topic finally cleared to me

You have received the debit note in the month of May, you will have to adjust that Debit note in May and file net GST output i.e. 15,000/- in GSTR3B of May 2020. Note that if you received debit not before filing April return, than also you can not adjust that in April, you must have to adjust that debit note in May only, because it's received in May.
also you have to fill the Credit Note (it's debit note from Party' against you have to issue Credit Note) of 10,000 and report that credit note details in GSTR 1 of May 2020 table No 9B and 25,000(Current month sale) in Table 4A of GSTR1 of May 2020.

If the credit note is received in April month.... then 10000 is to be mentioned in table no 9 of Gstr 1 or not after less this amount from the net sale of April......... in simple world.... what will be the treatment if the ...sales retun is received in same month in which sale is made...????

In GSTR3B You have to show your outward in Table 3 net of sales return.(i.e Sale bill minus Credit Note)

In GSTR 1 You have to show your B2B sale invoice in B2B sale table i.e table 4 and Also required to show b2b credit note in Credit Note table i.e table 9 sepratelly, whether its relating to sale of this month or earlier month's
B2C sale bill and B2C credit note : Net figure in table 7