It's up to you to find out, but it's not 100% certain to work.
Use this tool: link
1 - Download the jar and put it in the same folder as your keystore, then run the second command:
java -jar AndroidKeystoreBrute_v1.05.jar -m 3 -k sua-keystore.jks -d sua-lista-de-palavras.txt
I tested on a keystore in which I had put two words and three more numbers as a password, the first letter of the password being capital letter.
In my word list I just provided the two words that were in the password. The capital letter for the first one is automatically added as well as the numbers. In your list you put the words that you think would be in the password (if you think you have a date, put it also)
Your list may look like this:
primeiraPalavra
segundaPalavra
01032016
I received the following response when executing:
Got Password in 12 seconds
As well as the password and alias I used. Let running and good luck!