These links are set up in a table with the button in the background.   I've added borders to the table below so you can see the columns and rows....


To add a new row edit the 'table' link above and add a row. You can use this page to test your links on before you put them live.
If you put an image in first cell that is the same size, everything else should fall into place.
Little icon images are 60px X 67px you can create an image template for yourself in Google slides that will help you with the size.  The word links are simply typed in the cell and linked and show up on the background image of the button.
 Library Catalog link will open in new window.

I put a border on this image too.  It's a little larger than it looks, I used the icons you already had but resized them.

Below is the way you had them.  In case you want to go back to them.  As long as they clear the test, it will work.  I have used this type of buttons before and they can work fine. This new way may be easier to add new buttons, changes words or titles, and just use little icons.  The icon image is a .png with a transparent background.  You can set slides to save as png and with transparent backgrounds.  I made a slide you can copy and use as your own...

I hope this all helps.