In watlz, how does a lead indicate whether he wants the follow to do a heel turn or a reverse turn? They seem to start off the same.

Let's see lady's steps to know what's the difference from her point of view (always do this, because you want to 'manipulate' her by your leading!): At a heel turn Lady has to CLOSE FEET on 2, so after 1 she doesn't swing to the side but pulls her LF towards RF.
Because of this you have take care not to transfer your side swing between 1 and 2 to the lady, by taking weight a little longer over your LF e/o 1, so that she feels that she has to turn on one spot (the point where her RF arrived e/o 1). This may be felt as "releasing hold a little bit" BUT this effect of course must not be seen from outside the couple, because otherwise the dancing hold looks wobbly!

Actually it's far simpler than this.

The lady bends her arriving leg on step one of a waltz reverse, wheras in a heel turn she straightens it. The man must simply do the same thing: dance onto a straight leg being sure to create foot rise before the end of the step for step 1 of a heel turn, dance onto a softer leg with foot rise as the knee softens for step 1 of a waltz reverse.

By straightening her arriving leg as she arrives on it, her free leg will swing only to closed and not through. The lady does not "pull" her leg closed, because she doesn't "know" it's a heel turn - the man has to create a movement that will swing her leg closed without thought, and that movement is getting her to stand up in place by doing so himself.

Dear Anonymous,you did put them well. They are different . Straighten arriving leg is a good sign indicated what the step will be .
I practiced immediately the reverse turn in heel turn : RF backward without bending , press RF ball transfer the body weight toward the heel , just let the LF heel spontaneously close to RF reacting to step one , it looks as if smooth . Of course ,I am not sure if it works when dance with my coach. I thought there might be other technique to learn.

Logical thought: knowing the lady step first then holding on male left toe a little bit longer to allow for that she has to turn on one spot. Delay body weight transfering helps to distict the heel turn from reverse turn.
You provided a clear clue for thinking and solving the problem. Thanks.
I noted my reverse turn following feather step in foxtrot usually looks harsh . (I had ever tried to push my standing hip with my RF backward ( heel outward before touching the floor ), extend my left side with drawing LF at the end of bit one to create the space for man's RF. Both of us were unsatisfied. In my situation ( I am a beginer , a student .) the above-mentioned thought is unable to practice, I should solve it on my own way.:((