Mipeujioy95 The problem in this Client help Clients community is that there is not so much experience between us clients when it comes to business topics. So I can show, how to do as private client, probably the Combox for SME is similar. I go to "mySwisscom", there to "landline", and "remain available", clicking on that there is a button "Go to settings"

and there you can choose the option "forward all calls"

Possibly you can find a similar way on the Business telephony app, the link to that you may find herein:
Forward calls and stay available - Help | Swisscom
If not,you can contact the business hotline 0800 055 055
Product consultation: Fixed network telephony – Contact for business customers | Swisscom