May vitamin d3 is 23.1 ng/ml what is the recommended dose regime of supplemental vitamin d3 ( tablet, soft softgel ) to reach the optimum level and duration of taken the vitamin d3 supplement??

If your skin is dark, a supplement of vitamin D3 1,000 IU (25 mg)/day is enough to raise the level above 30. However, if you are white, you need 2,000 IU (50 mg)/day, because white people usually have a higher vitamin D level so baseline level of 23.1 implies a more significant deficiency. You need to take this vitamin supplement almost indefinitely unless your living conditions change later.