answering my own question I have since talked to tax professional as well as the bank(Charles Schwab) where is have the IRA as long as the check was postmarked on april 18 it can be applies to the previous year.
In my example I wanted to contribute money for 2021 tax. I was able to sign up for the account and mail it by the 18th and I applied for the 2021 tax year granted this may be different for different banking institutions but in my case it all worked out.
