Without knowing the country you come from and what kind of healthcare system you were in it's difficult to advise
Well, I do not know for sure but I would think you would be covered by the basic insurance because the accident happened before you became a Swiss resident and therefore it is more like a "preexisting condition". You could not have had "accident insurance" in the Swiss meaning of it if you were not resident at the time
Yes, but being abroad and not under the Swiss system that distinction has no meaning?
To the OP, in any case, the order of things to do is
A) sign up with the "commune" where you arrive to declare yourself resident (I presume you have your new address/rental or residential property and all that)
B) call the health insurance company you will sign up with and make the contract
C) clarify with them whether they cover your treatment under the basic insurance scheme - this should not depend on the company
D) go to the doctor, according to your new health insurance
Since steps A and B are non-optional, you might as well do them ASAP and then you can get a clear answer. If you need more help you can call the respective cantonal health authority which usually enforces basic insurance coverage