"加标点于" can be translated into English as "add punctuation to" or "insert punctuation into", depending on the specific context and the desired nuance.
"Add punctuation to" implies placing punctuation marks at appropriate places in a text or sentence.
"Insert punctuation into" suggests a more specific action of putting punctuation within a particular part of the text.
For example:
"Please add punctuation to this sentence." (请给这个句子加上标点。)
"You need to insert punctuation into the text to make it clearer." (你需要在文本中插入标点，以使其更清晰。)