Replaces part of text with specified text string

Syntax of Excel REPLACE formula:
=REPLACE(old_text, start_num, num_chars, new_text)

In words:
=Replace(part of this text string, starting from this position, replacing this many number of characters, with this text)

Examples of Excel Replace Formula

If cell A1 has ABCDEFG and you want to replace CDE with 123 then formula will be: