How do devices connecting to a switch with trunked ports, obtain dhcp from the router?

Please bear with me as my networking sill are quite basic as I've only started working in IT approx a year and a half ago and a more of a general IT Tech.

I'm working on a small migration, moving from physical host servers to office apps. They have a Windows DHCP server giving IP's for work stations and printers, I'm going to be configuring Cisco router to dish out DHCP for the workstations and printers.

I know the DHCP scope I'll be creating and can manage all that fine, I'm slightly confused on how devices connected to ports 1-6 for example, will obtain an IP address. The ports on their switches at the moment are mostly configured as trunk ports, with some ports configured as VLAN 7 for voice.

This network was all inherited and our Cisco experience is limited to null basically.

I can create a new VLAN2 and assign the correct DHCP scope to the VLAN, but when it comes to the ports on the switches I'm confused in how devices will know to obtain an IP address from VLAN2 in the 192.168.1.x range.

Will it just be the case of re-configuring the port and remove the trunk and just assign those ports to VLAN2? As this was inherited I'm not sure on the consequences, the ports are empty anyway so I would not of thought it would be an issue.