My registered mark may be attacked for non-use, or I want to attack one

A registered mark that is not genuinely used can be removed. The grounds and defences are narrow.

High complexity - significant legal consequences

Section 47 has two limbs: no bona fide use by any proprietor since registration, and the mark was registered without a genuine intention to use; or a continuous period of five years or more from the date of entry on the register in which there was no bona fide use by any proprietor, counted up to three months before your application.
The mark can survive if bona fide use on the same or associated goods or services is shown, and non-use caused by special circumstances in the trade, including legal restrictions, is not a ground.
Any person aggrieved can also seek cancellation or correction of an entry on other grounds under section 57. Since the 2021 Tribunals Reforms changes, applications under sections 47 and 57 go to the High Court or the Registrar depending on the provision. IP India's copy of the Act may still say Appellate Board, so ask an advocate which forum applies.
Gather dated evidence: market checks, website archives, investigator reports and absence of sales.

The honest answer usually needs someone to look at your actual disclosure, your timeline and the prior art. That is a conversation, not an article.