According to the UNITED STATES DEPARTMENT OF AGRICULTURE – defrosted food may be refrozen if thawed slowly in the refrigerator under sanitary conditions.
If raw or cooked food is thawed in the refrigerator, it is safe to refreeze it without cooking or heating, although there may be a loss of quality due to the moisture lost through thawing. After cooking raw foods that were previously frozen, it is safe to freeze the cooked foods. And if previously cooked foods are thawed in the refrigerator, you may refreeze the unused portion. Do not refreeze any foods left outside the refrigerator longer than 2 hours. If you purchase previously frozen meat, poultry or fish at a retail store, you can refreeze if it has been handled properly.
Read more from USDA:
https://ask.usda.gov/s/article/Is-it-safe-to-refreeze-food-that-has-thawed