If I understand you correctly you're setting your shift lever and chain to the middle chainring and then setting your cable tension. Try this. Screw the cable adjuster screw on the shift lever all the way in and then unscrew out around 3 full turns. Shift the lever to the lowest gear position (i.e. for the smallest chainring), Put your chain on the smallest chainring, pull the cable fairly tight with some pliers as it's a little difficult to pull the short length of cable with your bare hands, clamp the cable and it should work. Use the cable adjuster on the shift lever for fine tuning. There is also the possibility that you'll need to make some other adjustments which can be addressed in some " front triple derailleur installation/setup" videos. Park tools makes a good one. https://www.parktool.com/blog/repair-help/ There are many other good videos on this and some are even made by BikeForums members. You mentioned that watching some videos didn't help but keep looking until you find one that works for you.