well, there are two ways.
The hard and most expensive one is to sell all your players, buy 14 3* players and wake up early tomorrow (or stay up late ) and start building the new team.
The other way, is playing in a long term. That mean to keep your 0T academy players for many seasons. Of course it's a different way of playing the game because you need to keep 6 positions for those players plus maybe one extra free position for the new academy players you want to sign and sell.
So you must have 15-16 active players to go for the treble.
The good thing is that after 3-4 seasons, those academy players will be 1* players so you can have a very low q avg.
So, best buy 2-3 3* players.Next season they will be 2* and the next will be 1* players.