The repeaters are all on shared frequencies. For example, what's labeled "Channel 15" and "Channel 15R" in most radios (with the R suffix being a repeater) is exactly the same listening frequency.
What makes it a repeater channel is a +5MHz offset on the uplink.
What that means in essence is that if there's a repeater nearby transmitting on 462.550 (for example), you'll hear it on both Channel 15 and Channel 15R. But the repeater won't hear you unless you change to Channel 15R (Channel 15: TX/RX on 462.550. Channel 15R: RX on 462.550, TX on 467.550). But given that the vast majority of GMRS repeaters (at least that I encounter or are listed on RepeaterBook or here on MyGMRS) have a 'tone' set, you likely won't be able to just 'tune' to a repeater channel and then use the repeater. You'd need to identify the repeater, look it up, and program the tone in. At which point best practice is probably to create a 'new' channel specific to that repeater.
So tl;dr, the way you're currently scanning is probably the best way to scan. Otherwise you're scanning through redundant channels.
However, the actual answer to your question is to go to the repeater channels (15R, 16R, etc.), press 'Menu', and then scroll until you see "SCAN-ADD", then make sure that's 'ON', then those channels will be included in the scan. If that setting is already 'on', then you'll want to get the programming cable and connect to the software on a PC and adjust the 'Scan Groups' (or try to do that through the on-screen menu). But again, I personally wouldn't. You'll hear every repeater in range scanning as you currently are; adding the repeater channels to the scan group will just slow it down.
If you're interested in repeaters and don't already have a programming cable; I'd get one. Then program in local repeaters or those you think you'll encounter (999 memory slots; you've got lots of space). Then they'll be ready to go. I haven't tested it, but I believe if you set receive tones for those repeaters and then put all those repeaters into a scan group; you can scan JUST through the repeaters and it'll ignore all other traffic except for what the repeater is transmitting. (Meaning simplex communications that aren't a part of the repeater won't be picked up by the scanner)