Fixing converted score--wrong measure lengths

After converting a pdf to mscz, I find a few measures where the meter is wrong. Specifically, I have some measures that are 1/16 short, for example, because a dotted eighth lost its "dot". But if I edit the offending note(s) the entire measure breaks.
That is, in a score in 3/8 time, I have a measure with two eighth notes and a sixteenth note that has "lost" 1/16 of the measure time.
How can I "stretch" the measure by 1/16?
Using Musescore 3.5.2 on Mac OS 11.1