To unhide multiple hidden rows, please refer to the shortcut Ctrl+Shit+9 if you like using the shortcut or follow the steps below for details:
Step 1: Select the rows that were hidden (or select the whole worksheet by clicking the top left corner);
Step 2: Right-click and select "Unhide" from the dialog box;
Step 3: The hidden rows will show up.
Alternatively, please use commands from the ribbon:
Step 1: Select the hidden rows (or select the whole worksheet by clicking the top left corner);
Step 2: Clickthe "Home" tab from the ribbon;
Step 3: Click "Format" in the Cells section, and select "Unhide Rows" from the "Hide & Unhide" command.