Wiktionary
muddle up
vb. 1 (context transitive English) to confuse (one or more objects with another object or other objects) 2 (context transitive English) To mix together
Usage examples of "muddle up".
The next one was an old Eagles song that gave Stuart a chance to sing and muddle up the lead guitar riffs.
They're all born knowing just what it takes to find a way to muddle up your head.
I am not going to allow Madam Celeste to muddle up this investigation.