I need to use a pull request. How can I merge a single commit?

Based on your requirement, you can try the following steps to do the cherry pick in Azure DevOps:

Step1: Create a new branch based on main.

Step2: Navigate to Repos -> Commits -> Select the target One commit. Then you can use the Cherry Pick option to create a new branch based on the new branch in Step1.

For example:

Then you can select the branch.

Step3: It will automatically create a Pull Request and contain only one commit.

For example: From cherry pick branch to main branch

What exactly have you tried? I’d suggest using the shell for this:

# go to target branch
git checkout main

# find the hash of the commit to cherry-pick
git log dev
# the out put should be the history of commits with hashes <1> / <2> / <3> ...

git cherry-pick <2> # pick commit with hash <2> for example

git checkout main
git cherry-pick <commit-hash>
If any conflict resolve them:
git add .
git cherry-pick --continue

merge a single commit:
git rebase -i HEAD~(number of commit that you want to merge)
it apear a GNU nano : change pick to s or squash

I run :
git rebase -i HEAD~2

pick d6fa7b5 nth employee salary
pick fde8554 1st employee
.....

change pick to s:

pick d6fa7b5 nth employee salary
s fde8554 1st employee

press : Ctrl+X then Ctrl + Y,Enter,Ctrl+y

then all commit become a single commit.

Note : Sometime there are a validation to direct commit or cherry pic in main branch. After pull request it merged to main branch. please check this.