First: this is not an uncommon problem, and your school district should be comfortable with helping kids deal with this. I would expect that your teacher in first grade should've addressed some of this with you already, but perhaps this isn't such a big problem so far.
One successful approach they've used at my son's school is to use "wiggle chairs", which is a generic term for chairs or seat toppers that children can use which allow them to move around some while still sitting; think a non-flat seat that can move some, as they move their bottoms around the seat responds some.
Another good approach is to use a sensory device. Depending on the child, this can be a squishy ball, a ball with sort of spikes on it, a crinkly foil thing, a chewie (something the child has on their wrist or a necklace that they can chew), or many other things. This got a bit of a bad name due to the 'fidget spinner' craze, but regardless of that silliness, there is legitimate benefit to be seen for some children.
A third approach is to have the school consider accommodations that help your child specifically. This could include a standing desk (or simply being allowed to stand) if they can do so without disruptions; frequent breaks; adjusted schedules for certain things that can be adjusted within the classroom environment; or other accommodations as appropriate. Your school or school district should have a specialist who is familiar with children with these issues who can help.
Finally, you can consider occupational therapy. Some schools have on-site occupational therapists; others you may have to get this on your own. Occupational therapy is a sort of physical therapy that helps children develop muscles in ways that is helpful for addressing some of the issues related to ADHD and other similar challenges (such as your child may have). Developing core strength, for example, can lead to better attention skills.
I strongly recommend you look into some of these online, and then schedule a meeting with your school, either the teacher or your school's occupational therapist and/or specialist, or better - both. Talk to them and see what approaches are best for your child, and what the school can assist with. And keep with it - talk to them regularly and frequently. Have monthly meetings with the teacher or the therapist to see how things are going. The school appreciates involved parents who ask questions and want to know how things are going, because those parents are also the parents that are most likely to help their children succeed.