Did you have backups turned on with the S8? If so, then much of your data will be backed up with your Samsung account.
There might be data stored on the SIM card and your provider should be able to access that.
Getting you LG to work will probably require 1 or more calls/trips to your provider. The LG will need to be released by TMobile (if it can). Then you will need to get a SIM card that fits from your provider. (LG takes a micro-SIM and the S8 a nano-SIM). Then your provider will have to add the LG to their network. Then hopefully it will work ... or you will be on the phone with your provider's support some more.