Hello and welcome to the community. 
This is a false positive. It is not possible for a trojan to be embedded in a WeMod trainer.
False positives are triggered due to the way trainers work, which is by injecting values into your PC’s RAM that a game is running from. They are completely harmless.
More information: Windows Defender marked WeMod as a Trojan.
When you are logged out of your WeMod account (ie, due to your internet caches being cleared), you will be assigned a temporary guest account until you log back into your own account again. To do that, click the down arrow in the top-right of WeMod and select Switch User.
See here: https://support.wemod.com/article/90-why-am-i-logged-into-someone-elses-account.