Should be easy-peasy
Use a boat.
Use Animating Performance
Wait til you're 6th level.
Use Animating Performance. Tie a loop in a rope. Animate the rope. Hold on to the non-loop end. Tell it to go put the loop over the big white furry thing in the bottom of the water, pull the loop tight, then tug to let you know it's got it. Then you ought to be able to pull it to the surface, and the rest is just getting it to shore.
Okay, your DM's going to have to cooperate here. On the plus side, the Dancing Item is immune to exhaustion and it has darkvision. On the minus side, it's only 4 smart.
Your DM may tell you the rope's just not smart enough to loop itself around a big white furry thing.
No problem, but you're going to have to go in.
Animate the rope, tie it around you. Tell it, if I tug on you, take me back up and put me in the boat. Drop a weight on a rope down to where you think the yeti is. Pull yourself down and find the yeti. Tie a (different) rope to it. Tug the animated rope, go back up to the boat, pull the yeti to the surface.
The DM may tell you the rope doesn't have a swim speed.
Okay, tie the animated to the boat, put the loop around your upper body, then into the water you go. That way the rope's not swimming, it's just pulling you.
Also, tiny hut may be useful. If you cast it on the bottom of the pond.
Don't want to wait?
Going to be harder at 3rd level. Do the same thing with the weighted rope. Once you find the yeti, attach a net to it. Use Performance of Creation to create a buoy inside the net.
You can hopefully get back in the boat when you're cold and use something like prestidigitation to get warm (like warm your clothes or something). Or heat metal .
If at first you don't succeed . . . .
It make take multiple tries to come up with something that the DM will agree to.
Avoiding exhaustion
I tried to give you options to avoid exhaustion. Try not to stay in the water too long. You might need to find magical or mundane ways of staying warm in the water. Maybe smear lard on yourself before going in.
Locating the yeti
Maybe use speak with animals to talk to a fish. It's a stretch, but it might work.
Locate animals or plants might be helpful, but not directly, since the yeti is 1) not a beast, and 2) it's dead. Maybe you can find plants or animals to help in some way. Maybe a succulent water plant as a reward.
Locate object might locate the yeti. I think that's pretty legit. Just use it to find the nearest dead yeti and you should be set.
You might need help
Locating the dead yeti in the dark cold water and getting it out might be more than you're going to be able to do by yourself.
Get your fellow adventurers, find some friends, or hire them. Or perhaps just persuade them. Bards are good at that.
With multiple people you might be able to bring enough resources to bear to accomplish the task.
Hopefully the cold waters have preserved the yeti and it hasn't been eaten by something.
You can celebrate with yeti tartare, well aged. What's that? Oh, no thanks, I'll pass, really.