Project separation

I have a project for a STM32H7. The idea is to split the project into two separate projects. This is a functional separation. Can anyone help me what elementary steps are necessary to make these projects as follows:
One project should land directly in the flash, the other project will be loaded from an external flash into the ram via a bootloader(which exists!). Now both projects must still be functional.
I am aware that I must create appropriate headers, so that necessary functions must create that appropriate interfaces know each other. However, I have no idea how I have to adjust the linkerfile etc..