I think the only way to achieve that confidence is by having done it successfully MANY times in the past. I think, you have to win, A LOT. There is no way around it that I know of. No way to truly fake the kind of confidence you get from winning. I talked about this in a recent podcast interview with Kit Dale. Visualization can help, but only to a degree.
The great thing is: losing doesn’t have the reverse negative effect if you don’t let it. While losing hurts very much, for me it doesn’t seem to have a negative effect on my confidence. I just focus on the detailed mistakes that resulted in my loss, and work hard on fixing them.
So if winning adds confidence, and losing doesn’t hurt it, the formula for developing confidence in competition is simple: compete as often as possible.
Of course, there are a lot of reasons that competing is tough to squeeze into the weekly way of life for a recreational competitor: time, money, work, family, responsibilities, etc. But I find that people often assign more weight to each of those reasons than they ought to. There are always many local tournaments, and $80 is not that much money if you put that money aside and plan for it (financially, mentally, and schedule-wise) months in advance.