The 29-year-old didn't play in England's last two matches of the tournament. England lost their semi-finals to eventual champions New Zealand in Abu Dhabi.
The left-arm quick is now making a return and starred in two wins for Deccan Gladiators in the Abu Dhabi T10 played at Zayed Cricket Stadium.
"It's feeling good," Mills said after the Gladiators defeated Northern Warriors by six wickets on Tuesday.
"Obviously very disappointed to pick up an injury during the World Cup. It wasn't a bad injury. So, I knew it would be a couple of weeks. But, yes, it was very frustrating to miss the end of the World Cup. I am looking forward to getting back here for the T10. I am still easing my way into it. Getting my confidence back. It's nice to contribute to the win."
After missing out on the first two matches of the Abu Dhabi T10, Mills took two wickets against Delhi Bulls and one against the Warriors.
"I stayed with the England team in the UAE. So, I didn't go back to England. I stayed to support and do my rehab with the England physio. They knew I had this tournament coming up, if I was fit. They helped me prepare for that. When I arrived (for the T10) I told the coaching staff that I probably need just a few more days and that's why I missed the first couple of games. It is quite a long tournament. So, I am sure that I will continue to manage myself through that. I am being diligent and sensible."
In the second match of the day, Bangla Tigers thrashed Chennai Braves by nine wickets. The Gladiators are second on the points table with six points from four matches, behind leaders Team Abu Dhabi. The Tigers are fourth with four points from four matches, behind Delhi Bulls.
Northern Warriors: 70/6 (10 overs), Samit Patel (21), Abhimanyu Mithun (11 not out), Wanindu Hasaranga (2 for 5). Deccan Gladiators: 76/4 (7.1 overs), David Wiese (27 not out), Tom Moores (21 not out), Josh Little (1 for 5).
Chennai Braves: 90/6 (10 overs), Angelo Perera (26), Samiullah Shinwari (20), Benny Howell (2 for 22). Bangla Tigers: 91/1 (4.2 overs), Johnson Charles (36), Hazratullah Zazai (34 not out).