I have a table that is created outside dynamics AX.
When trying adding new record to AX, there is an exception that index exists (for the specific table, there are no unique indexes except recid.
How can I force a new sequence, that recid should start with it next time I try insert new record?
First of all you should never create tables in a Dynamics AX database without doing it through the Application Object Tree. It is an invite to maintenance problems of your AX database; or put in another way, a very bad practice.
Having said that, the table you are seeking is named SystemSequences:
This is a system table and protected by the framework. Use it with care.