Xiaomi deletes text messages every year.

If it is a 2.3 system, draw to the right in the conversation, and there will be a number of check boxes. You can delete all the conversations you want to delete in batches by checking √. The same is true for deleting short messages in conversations in batches.

If it is a V4 system, press and hold session/SMS for a check box, which can be processed in batch.