By default, the forms are installed in C:\Program Files\Autodesk\Autodesk Infrastructure Administrator 2024\Template\Modules\[Module Name]\Forms. For example, water model forms are in C:\Program Files\Autodesk\Autodesk Infrastructure Administrator 2024\Template\Modules\Water\Forms.
The custom forms are named using the convention IM_[Module]_FORMS.xml. For example, a custom water form is called IM_WA_FORMS.xml.