The deleted or modified changes will be under Changes tab. Right click on that change do revert change.
Hope this helps!
If you have not yet committed the deletion yet. the easiest way is to close Mendix Studio, rename the project's directory to something like ..._Broken. Open Studio pro again and redownload your project. This will download your project anew from sprintr.
If you have already committed your deletion, revert your most recent commit via 'Version control' => 'Reverse merge changes'.