Changes due to pregnancy are one of the reasons that surgeons suggest delaying standard abdominoplasty until after childbearing, but things don't always work that way.
Your pregnancy changes several things about your abdomen. The total subcutaneous and intra-abdominal fat content may have increased. If so, general weight loss / body fat loss would be the first intervention. If localized fat concentrations have developed, then liposuction would be an answer.
The pregnancy undoubtedly stretched the abdominal wall support layers again (muscle and fascia). Abdominal exercises / toning may be able to reestablish some of your gains from the prior abdominoplasty, but a revision surgery with new tightening of the abdominal wall may be needed to restore tone. Try the exercise first. Repeat surgery would also be necessary if you have developed significant loose skin. Your surgeon may design a procedure that is less involved than your prior abdominoplasty, combining muscle tightening with localized liposuction. An in-person examination will help determine the best recommendations.