Join calmly. Say the opening takbeer while standing. If you arrive during the first rakat's recitation after its extra takbeers, say the missed extra takbeers, then listen. If joining in ruku, the details depend on whether you can catch the imam; do not delay until you miss him.

If you missed a rakat, complete it after the imam finishes, with recitation followed by its extra takbeers. Under the Hanafi ruling, someone who misses the entire congregation does not simply perform Eid alone as a replacement. Seek local guidance for your situation.

Detailed Hanafi latecomer and missed-prayer guidance. Learn these cases with a teacher before Eid if you expect to arrive late.