It disappeared in some commit. Respective links are https://tracker.wikimedia.cz/export/ and https://tracker.wikimedia.cz/import/. It should be re-added as "button".
Per T193465#4695323. Also, please assign yourself only to tasks you're comfortable to mentor. I really don't think mentoring a task belonging to a project you never made a single commit to is a good idea.
Change 469865 had a related patch set uploaded (by Nathan fraignt; owner: Nathan fraignt):
[wikimedia-cz/tracker@master] Added import and export buttons.
Change 469865 merged by jenkins-bot:
[wikimedia-cz/tracker@master] Add import and export buttons.