“This service that you perform is not only supplying the needs of God’s people but is also overflowing in many expressions of thanks to God.” 2 Corinthians 9:12.
Apostle Paul voiced how proud he was of the believers in Corinth concerning their commitment to giving to other believers in need. (I feel the same about you. And just as Paul bragged to others about the Corinthian Church, I brag to others about your generosity to believers who are in need.)
In this chapter Paul compared giving to planting. He said, their seeds of giving will reap a harvest of increase for them, but it will also result in an increase of thanksgiving to God. When we give, it provides the answers to the prayers of others who are in need. It gives them opportunity to glorify God with thanksgiving.
This is how we sow (or sew in this case) seeds of thanksgiving.