SETE requires a browser with CORS restriction disabled to be able to login. You have more information in the FAQ of Sokker Asistente.
You can use the Android app of Sokker Asistente to make SETE work.
If you login, your tactics will appear instead of the default ones. This will allow you to select the one you want to edit it. Alternatively you can paste your tactic ID and open it in a popup to copy-paste the tactic letters to the tactic textarea.
"Mix" opens a popup with an auxiliary tactic that lets you pass the positions of the players of this tactic to the main one.
"Swap" allows you to swap two selected positions.
"Mirror" inverts the selected positions horizontally.
The textarea below the main tactic serves to transport the tactic from one user to another, or to save the tactic in a text file and reuse it at another time.
"Save" saves the tactics in Sokker. You must have previously logged into Sokker in another browser tab in order for Sokker to accept the changes. Unfortunately this is not available from the Sokker Asistente app.