Open an asset in the Lytho asset manager, click show more and edit the asset (by clicking the pencil icon). Open the permissions tab and start typing to search for the right permission tags.
Before adding permissions to an asset you have to make sure that the permission tags are added in the Lytho settings. Now, open an asset in the asset manager and click show more. Open the permissions tab and select the edit icon on the top right corner which activates an input field for permissions. Here you can start typing to search for the permissions tag you created earlier in the Lytho settings.
The permission tag added to this specific asset now only allows users in a permission group with this permission tag to view the asset. For instance: 'User 1' is in permission group 'A'. This user can only see an asset with permission tag 'Lytho' when this tag is added to permission group 'A'.