You should probably use readtable or readmatrix since xlsread is deprecated.
You should probably plot one or more curves first, before asking the user, so they know what values of Datum to specify.
To ask a user for two floating point numbers, see this snippet:
% Ask user for two floating point numbers.
defaultValue = {'6.3.2020', '18.3.2020'};
titleBar = 'Enter values';
userPrompt = {'Enter date 1 : ', 'Enter date 2: '};
caUserInput = inputdlg(userPrompt, titleBar, 1, defaultValue);
if isempty(caUserInput),return,end % Bail out if they clicked Cancel.
% Convert to floating point from string.
usersValue1 = str2double(caUserInput{1})
usersValue2 = str2double(caUserInput{2})
You might want to convert the dates to numbers to get the row index of those dates. They've been changing the date manipulation functions so much over the past few years, it's hard to keep track of the best, recommended functions to use to do that so you'll have to do a little research on that.
