@leanne Ok I figured it out actually!, for anyone who is quite new to Retropie like myself, this is the command you must enter:
sudo nano /opt/retropie/supplementary/splashscreen/asplashscreen.sh
which will open a script so that you can edit a line that may look similar to this:
omxplayer -o both -b --layer 10000 “$line”
And change both to alsa:
omxplayer -o alsa -b --layer 10000 “$line”
It worked for me, hopefully it will work for you!