Command string items from mainUI

I am new to openhab3 from openhab2.5 .I see that commanding switch items from mainUI is possible but how can i send a command to a string item like i did with PaperUI?Is it possible ?

Sure. Create a page with a widget, then use action and actionCommand like in this YAML example.
Yes that’ll work with strings, too.

- component: oh-label-item
    action: command
    actionCommand: ON
    title: NeuinitialisierungEnergiemanagement
    icon: oh:error
    subtitle: setzt das System zurück
    actionItem: Neuinitialisierung
    actionFeedback: System wurde neu initialisiert
    item: Neuinitialisierung