Same as 'to dent' — to make an indentation or dent in something. Also used figuratively to make someone feel down.
重い機械が落ちて床を凹ませてしまった。
A heavy machine fell and dented the floor.
彼女の批判が彼の自信を深く凹ませた。
Her criticism deeply dented his confidence.
子どもがボールを投げて窓枠を凹ませた。
A child threw a ball and dented the window frame.