See the documentation of eglot to know how to configure it.
Once you get eglot to work, you can use Citre in any buffer managed by eglot.
Citre only adapts the finding definition/reference abilities of Eglot, as auto-completion and imenu integration is done by eglot itself.
Eglot backend doesn't support finding definitions/references for a user
inputted symbol, so citre-query-* doesn't work. Tags and global backend will
be used for them if Citre could find a tags file or global database for the
current project.