apply for IPA letter

Is it possible to apply for new IPA letter
During lockdown

You do not apply for an IPA letter. That is not possible.
If you mean applying for a work pass (EP or S-Pass), then yes: It's possible that an employer who wants to hire you applies for your work pass - no changes to the situation before lockdown, just being approved became more difficult.

I have my IPA letter but i cant enter to singapore
EA told that he will extend the time my IPA letter is it possible

This is a completely different question!
Yes, the employer can extend the validity of your IPA.

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