Spouse is a green card resident since March 2020 and just recently got his SSN. How do I finish filing our joint taxes before October 15th?

During tax time I received great advice on here about how to file Married Filing Jointly with me as a US citizen and my husband as a new green card holder without a SSN. Now that we have successfully obtained his SSN, I would like to know how I'm supposed to update that information with the IRS? Do I need to amend my tax return or mail something else in? Thank you in advance!

 

This is the thread where I originally posted my question:

Tax law states because you are married, you must file you...