MG's Notes

1. Double-click the cell in which you want to insert a line break
2. Click the location where you want to break the line.
3. Press ALT+ENTER to insert the line break.

(source https://support.office.com/en-us/article/Insert-a-line-break-in-a-cell-a918e875-625e-4510-86d7-9f5873fe21c7)