Hi
I am a mountain biker and recently added sa gravel bike. I have a Trek Checkpoint but find control difficult with the handlebars, little flair. Any suggestions where I begin , my priority is control, the gravel races trails are fairly rough
Yes. Fit biggest tires that physically fits the frame. That way you will be able to go straight line more often, not worry that much about minor obstacles and also be able to lower tire pressure.
Any magic with stem & handlebars combo will not do much. It is just a road bike used in rought terrain. Get used to that type of handling is my best advice 
I’m a mountain biker that turned to gravel a few years back. I had a Checkpoint and now I have the Checkmate. I started off with 440 mm bars and now I’m down to 390 mm bars with the hoods turned in to about 375. I never owned a drop bar bike before, so getting used to it took time.
First, I would highly recommend getting a professional bike fit, it changed a lot for me. Then it becomes just getting time riding the gravel bike. Eventually those MTB skills will pay off and translate to gravel riding. I went from drop bar noob to being one of the fastest downhill, particularly in sketchy terrain. Now I look forward to fast and/or sketchy sections in races to move ahead .
Regarding equipment, get 50+ mm tires and run them at low pressures. For example a 170 lb rider with 50’s should be in the mid 20s for psi, depending on you and the system weight. With larger tires and lower pressures this should help control.
The one difference from MTB to gravel is that generally the gravel is more loose over hard. So unlike MTB where the tires will hook up and allow you to rail a corner, that’s not really a thing in gravel.
I went from road style bars with no flair to gravel bars with flair and angled outward drops and feel it made a big improvement in handling and confidence in the drops descending and cornering on rough loose terrain. I used to be somewhat reluctant to use the drops in these situations but now prefer it over staying on the hoods. In use, my hands are actually forward in the hooks to be able to keep one finger on the brake levers. Angling the hoods inward helped get the lever in a good position for this. Here’s the bars I got.
Just today I installed Ritchey comp beacon 35 degrees flares 
. I am in love. Much better control, geometry is really the closest thing you can get to MTB feeling. Drops are much more useful and comfortable. It’s easier for me to reach brakes and gears, much easier. Super comfortable on the downhills. I actually rode all the time on the drops (rarely do so), felt like riding a Harley Davidson. I am so happy with it. It’s not much aero neither am I. This handlebar alone makes me to can’t wait for the next ride. My handling is better, riding hoods feels better, but I can’t keep myself from riding these shallow flared drops so much comfort.
I agree fellow “flared drop bar gravelist”. I had Seido tackle bar with 25 flares and made no difference, but comp beacon did with 35 flares.