"The sample rate of the two audio tracks is different" I'm trying to merge a few video files through mkvmerge but I get the following error after running

mkvmerge -o '/home/videos/marged/new.mp4' '/home/videos/intro.mp4' \+ 'old.mp4' \+ '/home/videos/intro.mp4'


Error:

Error: The track number 1 from the file 'old.mp4' cannot be appended to the track number 1 from the file '/home/videos/intro.mp4'. The sample rate of the two audio tracks is different: 44100 and 22050


Is there a way to force this? If not how can I change the audio to the same rate as old.mp4 in ffmpeg for /home/videos/intro.mp4
To force to 44100 Hz, command template is

ffmpeg -i old.mp4 -map 0 -c:v copy -c:a aac -ar 44100 new.mp4