Hi @seobi1111,
To add text to a button, one should call the lv_label_set_text() function. For a "normal" button, like this, when adding text in two different lines like this, the generated function is as follows:
lv_label_set_text(ui->screen_btn_1_label, "1st line\n2nd line");
For the imgbtn widget, the textbox under "Attribute" in GUI Guider does not allow you to add line breaks, but you should be able to edit the lv_label_set_text() function that corresponds to the imgbtn widget and add a "\n" manually to see a line break on the imgbtn.
I hope this helps,
Edwin.