By “kinsman,” understand the גאל gā'al (Ruth 2:20 note).
Related Commentaries of Ruth 3:12
Ruth 3:12-13
12 And now it is true that I am thy near kinsman: howbeit there is a kinsman nearer than I.
13 Tarry this night, and it shall be in the morning, that if he will perform unto thee the part of a kinsman, well; let him do the kinsman's part: but if he will not do the part of a kinsman to thee, then will I do the part of a kinsman to thee, as the LORD liveth: lie down until the morning.