Where is alt tool (in order to create an "If else" condition) in IBM Rational Rhapsody in a Sequence Diagram?
P.S. Preferably with an example.
Suggestion: Is it correct to use Guard conditions (or simply Guards) before a message? (Like this: [Guard Condition] message) And if yes, can this solution be used rather than alt fragment?
Rhapsody tools:
Edit: I finally used Interaction Operation tool and it seems that it works for if condition, but I do not know how to add the else to achieve something like this: link
Related question: How to show "if" condition on a sequence diagram?

You can add an Operand Separator to your Interaction Operator and specify separate conditions in each part of the Interaction operator (see an image of a simple example here).
Please follow the instructions in the official documentation.