Reservations are not tickets and are separate from your pass. They will never show in your pass and need to be either on your phone or printed out.
It will be much easier to stick to the terminology -
Your tickets ( i.e.your pass) are vouchers to travel on the trains listed in your travel days and sent to your pass to accompany the QR code for that day.(see below)
Reservations are simply vouchers to take a specific seat on the train you are catching. In some cases a reservation is mandatory and is extra to the Global pass - this is what you get from reservation suppliers like b-europe. When needed these are always additional to your Global Pass.
Some trains have voluntary reservations (useful at busy times) and many like TERs have no reservations available, so just add either of these to the trip and then to pass and go.
I assume you have figured out that you put your planned trains into “your trip” in the app. Then before you board the train you operate the little slider to move it to your pass/ Then you click the show ticket button and it creates your ticket, which is a QR code and a written description of the train route and times. Until the slider is moved you do not have an active ticket.
If your plans change before travel simply slide it back and add any alternatives = right up to boarding.
If you board extra trains throughout the day you do the same process of adding them to your trip (if they are not already there) and operating the slider. This adds the new train details to your ticket and so on.
Your reservations are totally independent to your pass. For trains with compulsory reservations you have to present the reservation along with your pass. If you have a voluntary reservation that is used for finding your seat, but not needed for inspection to travel.
Obviously buses are not included in your pass unless they are rail replacement services.