回复:谢谢pijiang老师! but more questions...
On your H-1 approval notice I-797, there are validity dates in "Notice Type" section, which will tell you whether or not it is still valid.
If you still want to work for the sponsor (Petitioner) in H-1, just take valid I-797 to apply visa at border.
If you want to change to other employers under H-1, file I-129.