If you want to keep the same extension number you need to delete the softphone first.
If not :
Softphone extension : 1111
If the current license is full you will not be able to change it to multidevices but this is not an issue for now.
On Micollab, add a new deskphone extension 2222 multidevices license type.
On Mivb side, multidevice group, create the pilot number 2222 then add the softphone 1111.
On micollab side the 1111full license will move automatically to multidevice.
Now in micollab service, choose 2222 as deskphone and 1111 as softphone.
According the micollab client state (in office) ring my group, you can make ringing both extensions. But you only by calling the pilot number 2222
You need to konw that it's not possible to call separately deskphone and softphone for the same user. You need to call a pilot number, usually we create deskphone 1111 ans softphone 1*111 but you can call only use 1111
If you want to call separately, you need to create a second user with a different extension but you will lost many multidevices or full licenses so this is not the best practice