The 30-year-old Wales international told a Stradey Park press conference on Tuesday, "We were very disappointed with the way we played in Edinburgh. The way we'd practised was good and we understood the elements we needed to put into our game but as a group we didn't turn up and made too many errors.
"We're determined to put things right this weekend - everybody in the squad knows we've got to get our tactics, aggression and attitude right and that we need to play a high-skill game."
On his own game, Thomas said he was content but far from complacent. He said: "I've been reasonably happy with my own form and I'm really happy with the set-up here; we're learning a lot from the new coaching team."
Scarlets head coach Nigel Davies has prepared his squad for the latest big Scots challenge.
"It's a tough ask to go up to Scotland. It's not a place we've had much success in the past.
"We've had a pretty stern week reflecting on last weekend and I expect a far better performance from us this time. As coaches, we've changed the way we prepared the squad.
"There's nobody more disappointed than the players about Edinburgh and they're very focused on getting things right this weekend."
The Scarlets are without the injured Deacon Manu, Dafydd James, Mahonri Schwalger, Darren Daniels and Kees Meeuws.
Kiwi centre Regan King is back after a strong half in Edinburgh which followed three games out injured. Outside-half Stephen Jones is in having recovered from a knock to the knee at Edinburgh. Llanelli RFC prop Aled Hopkins could get a chance to shine, starting on the bench.
Scarlets: Ceiron Thomas; Mark Jones, Regan King, Gavin Evans, Jon Davies; Stephen Jones (capt), Martin Roberts; Iestyn Thomas, Matthew Rees, Phil John, Lou Reed, Scott MacLeod, Dafydd Jones, David Lyons, Gavin Thomas.
Replacements: Aled Hopkins, Ken Owens, Vernon Cooper, Nathan Thomas, Sililo Martens, Rob Higgitt, Darren Daniel.
Referee: George Clancy (IRFU)