BepInEx must be setup at manual or with r2modman/Thunderstore Mod Manager.
Create a file called Environment.props
inside the project root.
Copy the example and change the Valheim install path to your location.
If you use r2modman/Tunderstore Mod Manager you can set the path too, but this is optional.
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="Current" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<!-- Needs to be your path to the base Valheim folder -->
<VALHEIM_INSTALL>C:\Program Files (x86)\Steam\steamapps\common\Valheim</VALHEIM_INSTALL>
<!-- Optional, must to be the path to a r2modmanPlus/TMM profile folder -->
<R2MODMAN_INSTALL>$(AppData)/r2modmanPlus-local/Valheim/profiles/Develop</R2MODMAN_INSTALL>
<!-- Optional, deployment destination folder (this base folder must already exists) -->
<!-- If not set, no files will be copied -->
<DEPLOY_FOLDER Condition="Exists('$(VALHEIM_INSTALL)')">$(VALHEIM_INSTALL)</DEPLOY_FOLDER>
<DEPLOY_FOLDER Condition="Exists('$(R2MODMAN_INSTALL)')">$(R2MODMAN_INSTALL)</DEPLOY_FOLDER>
</PropertyGroup>
</Project>