Purchase return (Debit Note)

if you received debit note (purchase return) than you show your ITC in 3b less tax of debit note in the total purchase tax for this month

example..

if in this month your itc 200 in cgst and 200 in sgst and you recd a debit note (purchase return) tax 30 in cgst and 30 in sgst

so you show your ITC in 170 (200-30) in cgst and 170 in sgst
.

What if exceed return obtain?

explain your query plzz