Follow the steps for Custom infotype creation and Screen assignment for that new custom Info type :

1) Go to Transaction PM01.
2) Enter the custom Infotype number which you want to create (Should be a 4 digit number, start with 9).
3) Select the `Employee Infotype’ radio button.
4) Select the `PS Structure Infotype’.
5) Click on Create. A separate table maintenance window appears.
6) Create a PS structure with all the fields you want on the Infotype
7) Save and Activate the PS structure
8) Go back to the initial screen of PM01.
9) Click on `All’ push button. It takes a few moments.
10) Click on `Technical Characteristics’ . Infotype list screen appears
11) Click on `Change'(pencil) button
12) Select your Infotype and click on `Detail’ (magnifying glass) button
13) Give `T591A’ as subtype table
14) Give `T591S’ as subtype txt tab
15) Give your subtype field as subtype field
16) Save and come back to PM01 initial screen
17) Click on `Infotype Characteristics’ . Infotype list screen appears
18) Click on `Change’ (pencil) button
19) Click on `New Entries’
20) Enter your Infotype number and short text
21) Here we have to set different Infotype Characteristics as per the requirement. (Better open another session with some standard Infotype’s infotype characteristics screen and use as the reference to fill yours)
22) Save your entries.
23) Now the Infotype is created and ready to use.
24) If you want to change the layout of the Infotype as per your requirement.
25) In the PM01 initial screen.Select `Screen’ radio button and give 2000 as the screen name, then click on edit.
26) In the next screen.. Select `Layout Editor’ and click `Change’.
27) Screen default layout appears.here you can design/modify the screen.. change the attributes of the fields. etc.
28) Save and activate. (Don’t forget to `Activate at every level)