I have many fasta sequence files (separate) such as AF069756.1, AF069757.1, AF069737.1, etc. to be aligned. Is there any online tool where I can uploaded these files separately and can be aligned.
If you want to align your sequence one by one with your target sequence try Pair-wise alignment method. If you need to align more than two sequence with your target sequence try multiple sequence alignment. Visit the below link for more information and tool access.
Since you are mention the sequence accession, it seems like you downloaded it somewhere. Thus few things can be done.
1. If you are already having data and are familiar with basic command line operations, you can use cat command
Terminal$ cat *.fasta > all_sequences.fasta
(Note that * means everything, so the directory must contain only the files which you want to merge).
2. Copy paste the fasta sequences in a single file.
3. Go to NCBI and search the range of sequences (if they are in continuous order)
Search -> ABC123410.1[accn]:ABC123450.1[accn]
...thus will give the search result for range of 40 accessions, download it as fasta sequences.
Once you have all sequences in single file (multifasta file), you can use any multiple sequence alignment program online (just google, there are tons on them).