1 Open Steam and click Library.
2 Right-click on Valheim then click Properties.
3 In the Launch Options field enter -console.
Valheim guide
How To Enable The Console For Valheim
Valheim server owners may want to be able to access the in-game console to run certain moderation commands on their server. In order to do this they will first need to make a change to Valheims startup parameters on Steam. Once enabled the console can be opened in game by pressing the F5 key.