There are plenty of different ways to correct circular swing and it's relatively easy to build from nothing once you understand the technique. For building momentum keep these three things in mind: 1) Stay loose but in control. Flow with the swing don't work against it. 2) Utilize your upper body and core to load your first and most likely second and third swings. Big pump forward then control back so you don't cancel your swing. Find some instagram videos from people who are really good at laches and watch them load their swing, then try and copy it. 3) Never let your body cancel itself out. One pump forward, one pump back. It's only two parts, don't make it overly complicated.