You don't use RSA to encrypt long messages.
The correct approach is using hybrid encryption instead:
- Generate a random AES key, encrypt the actual data with AES. Preferably using an authenticated mode like AES-GCM.
- Encrypt the AES key with RSA. This key (126 to 256 bits) is small enough to fit within one RSA block. For example using small and thus weak 1024 bit RSA keys you have 500-700 bits for the actual data (the rest is consumed by the padding).
The ciphertext consists of both the RSA encrypted AES key and the AES encrypted file.
It's essential for security to apply padding here, namely OAEP. Most other paddings, including the popular PKCS#1v1.5 padding are not secure.
Don't try to split the file into blocks which you encrypt with RSA. There are no standard ways for doing this, because it's a bad idea.