T2-General: Sponsors license revoked

Hi,
I am currently under T2-General and my sponsors license revoked in the month. And as far as I know my curtailment end period is June 24th. I found an employer who is happy to hire me and he has got the license to sponsor. Myself and my sponsor is not aware of how to assign the COS and which category to choose. Need some guidance so that I can successfully make him assign a COS on my name and then apply visa.

1) I need to know whether he should select T2-Extension or T2-change of Employment in my case.
2) How long will it take to assign a COS on my name.
3) Also provide me the correct type of Visa form that I need to use as I am going to opt for the premium service
4) Can all this be done without a solicitor or should I mandatory need a legal advisor since my case is very critical.

My curtailment period is nearing so I need quick help. Please reply to me ASAP

1) I need to know whether he should select T2-Extension or T2-change of Employment in my case.
Should be change of employment
2) How long will it take to assign a COS on my name.
Your sponsor must assign unrestricted COS so it will take 30 mins or so, provided they have COS allocation.
3) Also provide me the correct type of Visa form that I need to use as I am going to opt for the premium service
You must select Tier 2 general
4) Can all this be done without a solicitor or should I mandatory need a legal advisor since my case is very critical.
Your sponsor must be in-line with home office rules, especially with RLMT, correct SOC code, and salary, if your sponsor does not follow then your visa will be rejected. Since your leave ending soon, I advice you take help from experienced immigration solicitor.