First, syncing from scratch is generally advised because it is faster. Second, you can find instructions here:

> Alternatively: if you want to grab the bootstrap (NOTE: there is a new bootstrap format!) off the website then you can get it at https://downloads.getmonero.org/blockchain.raw - once downloaded you can import it with blockchain_import --input-file /path/to/your/download.raw. If you're particularly brave you can pass the --verify 0 flag to skip verification during import.