Numbers 15:30-31 says there is no forgiveness for intentional sins. Is there forgiveness for intentional sins? What can we do to make up for them? thank you
The verse you mention discusses idolatry, and it writes that one who sins intentionally cannot procure the atonement of bringing an offering. However, even for the sin of idolatry, it does not mean to imply that true repentance will not help, and if a person fully repents, deeply regretting his deed and returning to Hashem, then he will be forgiven (see Sefornu, who mentions that repentance out of fear may not be sufficient; see also Tzror Hamor).
Many great Jewish leaders over the centuries have written explicitly (based on writings of the Sages) that there is nothing that can come in the way of repentance (the wording is from Rambam, Laws of Repentance 3:26; see also Shaarei Kedusha 2:8; Rama of Fano, Tikkunei Teshuvah 1; Shelah in many places, and so on). The Gemara writes that even Elisha (Acher), who sinned and brought many to sin, would have been accepted had he repented. The gates are never closed.
Together with wholehearted repentance, one can add one’s own personal “tikkunim” to atone for sin, for instance by focusing on the limb with which the sin was committed, by fasting, and so on.