I am unable to find the way to add customfields to a user in solarwinds servicedesk
Hey there Are you referring to Custom Properties?
First, make the field(s) you want (Setup > Service Desk > Custom Fields) making sure to use the Global scope.
Next, create a custom form for Users (or edit if one already exists in Setup > Service Desk > Custom Forms).
Finally, create a dynamic form rule with the scope of Users (Setup > Service Desk > Dynamic Form Rules) and an action to show the custom form you created.
If you don't see Users in the scope menu for dynamic form rules and you are on ESM, I've noticed the Users scope is only available at the Organization level and not on individual providers. The custom fields, custom form, and dynamic form rule should all be made at the Organization level