Hi @farshadhadei, welcome to the LE community forum 
There is a topic dedicated to this: Help thread for DST Root CA X3 expiration (September 2021)
Also have a look at the video posted here: Join us and learn about certificate chains! - #35 by jple
Also do notice this update: Help thread for DST Root CA X3 expiration (September 2021) - #198 by xnox