To Cut Oleander, you have to trim the main stem of the oleander once it is young. You need to Wait until the stem has developed two separate sets of leaves and trim it back to just above the first set. You must Snip the branches at a slight angle with pruning scissors. After that, wait until new shoots grow from the cut-off main branch and each one has two sets of leaves. You should cut each of the three shoots back to just above the lower set of leaves to encourage more branches.
You can continue repeating this process until the oleander is round, full and the size you want it. Then, trim back the oleander as needed to maintain the shape and size you want. You have to Snip off new growth each year with pruning scissors after the flowering is completed for the season. Next, cut out dead stems back to the live shoot it is attached to. If the entire branch is dead, you must trim back to the main trunk.
You need to Use pruning scissors or loppers to make the cut.