Accessing channels is done through zone lists. The up/down arrow keys selects the zone list; the knob atop the radio selects the channels within each zone list.
You can place up to 32 channels in a zone list. With two VFOs, you theoretically could have 64 channels in a zone list if you have an equal number of UHF and VHF entries.
Let's back up. Construction of a code plug: contacts > channels > zone lists.
I suggest you read
Amateur radio: DMR - 3 as an overview of a codeplug.
A second article to read:
https://www.jeffreykopcak.com/category/amateur-radio/dmr-in-amateur-radio/
I suggest you download a sample codeplug and look at its organization. I have some links to 9 sample codeplug sites at
Amateur Radio but note the the MD-UV380 file structure is NOT the same as an MD-380.
If you opt to look at an MD-380 codeplug, you can make a structural conversion to the MD-UV380 file format by using the
N0GSG DMR Contact Manager Support Page software. Be sure to read the PDF user manual first.
I have an MD-UV380. Perhaps the other notes and links will give you a jump start. Hope this helps.