To manually reserve equipment for a project, you can do this in the equipment's timeline. You can access the equipment's timeline by either opening the timeline in the equipment module or inside the project's equipment tab.
Once you have access to the equipment's timeline, you can reserve equipment on a certain project by double clicking the project itself > Reservation sources > edit number of equipment you want to reserve for project. See screenshot below:
You can change your equipment allocation between projects when periods overlap. In this case, you can remove your items from "Project A" and assign them to "Project B". Select the amount of equipment you want to reserve from your warehouse stock by setting a number in the “reserved for project” field and save.
Please note that depending on the project's status, equipment reservation will be affected differently.