Convert a string value from a T-SQL table in float values and store them in a second TSQL table [on hold]

I have a TSQL table from which I need to copy a column in a second table. The values that I need to copy are stored in the format 4444.44434 as a string But first I have to split the String into 4.444,4.4434. Then I store the value in the second table.

Now I do not know exactly how to split the string from the first table and then store them it in the desired format in the second table.

I am very grateful for any solution.

My Code so far:

SELECT String, LEN(Matchcode) as Length, 1 as Counter, 0 as Value1 From Test.dbo.tdValue1 
WHILE Counter <> Length { 
String.Index = Length - Counter if ISNUMERIC(String.Index) = 1 
{ LEFT JOIN tdValue1 ON tdValue2.String1 = tdValue1.String; 
Counter += 1 
    }
}