So I import my old adress sucessfully!
But now my coins appears in read only mode, so I'll try to import private key address, but an error occured like 'invalid private key format"
If you have imported an address from visiting a blockchain explorer, you have created a watch-only wallet.
You basically added this specific public address on a 'watch'-list inside your wallet.
You will not be able to spend funds associated to this address without the corresponding private key.
So how to convert private key to the new format?
If the string you have tried to import into the private key field did start with a 1.., 3.. or bc1.. it was an address, NOT the private key.
In this case you can not convert anything since this is not a format issue.
You need the private key to be able to access the funds.