Ascii values from 32 to 126 contains Numbers[0-9],Alphabet[A-Z/a-z] and acceptable special characters.
So you can check each character of your string to have this ascii value and if not then remove that character.
You can create a function of below code and use it to check each row of your table
Declare @Str varchar(50)='Hi you …there'
DECLARE @Result nvarchar(max)
SET @Result = ''
DECLARE @char nvarchar(1)
DECLARE @charpos int
SET @charpos = 1
WHILE @charpos <= LEN(@Str)
BEGIN
SET @char = SUBSTRING(@Str , @charpos, 1)
IF ASCII(@char) >=32 and ASCII(@char) <=126
SET @Result = @Result + @char
SET @charpos = @charpos + 1
END
select @Result