How to tie identical chords to extend duration

Hello, noob here.

Musescore 1.1 on Linux 3.0.0-12 / Ubuntu 11.10.

I went through the “row-row-row your boat” 10 vid tutorial. Went great. Thank you for those!

On my very first project I want to enter a 4/4 piano piece (two staves, bass/treble clef) that I wrote in pen years ago.

In the right hand (top stave, treble clef) 16 eighth note double stops (two note chords). Four groups of four eighth notes across two measures.

Now, what I really want is quarter note double stops at the and of 2 (through the down of 3). That is to say a quarter note straddling the middle of the measure between beats 2 & 3.

Also, the same concept for the and of 4 through the down of 1 in the second measure.

I do not want a quarter note in the middle of the bar and, obviously, this doesn't even make sense for the and of 4.

I would like to tie these eighth note double stops.

Is there a video that shows how to tie chords. The chords are identical I just want to tie them to alter the duration.

(I've tried on my own. I'm able to tie single notes, but not double stops).

Thank you in advance!
Stan.