Endovenous ablation causes obliteration of superficial veins - great saphenous or small saphenous (short saphenous) or perforator veins. If you can palpate (touch) a hard spot that is red, warm and tender, it means that a superficial tributary (branch) of the saphenous vein has closed and since it is close to the skin, you are able to feel it. If it is the saphenous vein that you are able to palpate, there is no need to do sclerotherapy as the vein is already 'closed' or obliterated or ablated. If the vein that has been ablated has recanalized (reopened), the doctor may be planning to attempt to reclose (ablate again) with sclerotherapy.
A better strategy would be to wait for the inflammation (phlebitis) to subside before anything else is done.