I have finished MS and I have applied for H1 while I was working on OPT. While I was in India I received the I797B notice of Action which mentions that my I129 petition was approved but I have to appear at a US consulate for COS from F1 to H1.I came back to US on OPT assuming I can apply COS here.After OPT expired in Feb I converted to H4.
1.If I want to work with the old employer can I change my status while Im in the US using my previous I129 approval? If so which application would they use to file COS. Other options?
2.If I find a job with a new employer can I still file for COS based on my previous petition?
3.If I find a job in a different field other than the field for which the petition
was approved can I still file for COS using the previous H1 approval.

Thanks